1. Field of the Invention
The invention pertains to an apparatus, comprising drive means for moving components of said apparatus and further comprising an arrangement for collision protection.
2. Description of the Related Art
An apparatus of said kind is described in the European Patent EP 0 087 198 which corresponds substantially to U.S. Pat. No. 4,578,757.
In the cited reference an x-ray examination apparatus is described that comprises an arrangement for collision protection based on calculation of distances between mutually moveable components or bodies and comparing said distances with safety distances. A collision is considered imminent in the known x-ray examination apparatus when a distance between components of the x-ray apparatus becomes smaller than a predetermined safety distance. Collision protection is achieved in the known x-ray examination apparatus in that movement of said x-ray examination apparatus is terminated when a relevant distance becomes smaller than the safety distance. The arrangement for collision protection as described in the cited reference aims at preventing collisions between components of the known x-ray examination apparatus. Therefore, a patient to be examined by way of a known x-ray apparatus is protected only from experiencing collision with a component of said x-ray examination apparatus when there are provided sufficiently large safety distances from a patient table that is a component of the x-ray apparatus. As a consequence, in the x-ray examination apparatus as described in the cited reference, required patient safety prohibits that the distance between a patient that is to be examined and components of the x-ray apparatus, in particular an x-ray image intensifier, can become arbitrarily small. Hence, spatial resolution of an x-ray image produced by the x-ray image intensifier is compromised by the requirement that an input screen of the x-ray image intensifier should be kept at least a safe distance away from the patient.
It is inter alia an object of the invention to provide an apparatus, such as an x-ray examination apparatus or an industrial robot, comprising an arrangement for collision protection allowing arbitrarily close approach of components of said apparatus, mutually, or of any of such components with a patient that is to be examined, or a person being within a reach of a component of the apparatus.
This is achieved in that such an apparatus, in accordance with the invention is characterized in that the arrangement for collision protection comprises power and/or current measuring means for determining (a) value(s) of power and/or current supplied to the drive means, and comparison means for comparing said determined value(s) of power and/or current supplied to drive means with (a) reference value(s) for said power and/or current supplied and for generating a first drive-disengaging signal for controlling disengaging a relevant component from the drive means.
For the alternative motions of components of an apparatus in accordance with the invention, the power supply required by the drive means under normal circumstances can be measured and thus reference values for the required power supply are known. Should a collision occur of any component of the x-ray apparatus with another object, e.g. with another component of the x-ray apparatus or with a patient that is to be examined, then the motion of the colliding component meets additional resistance and therefore the power supply required by the drive means would increase beyond said reference value. Detection of the required power supply, and subsequently comparing with a relevant reference value provides for generating a first drive-disengaging signal for interrupting the motion of the colliding component, and thus preventing the collision to cause damage or injury.
A preferred embodiment of an apparatus in accordance with the invention is characterized in that the arrangement for collision protection comprises current measuring means for measuring current supplied to the drive means, and current comparison means for comparing (a) measured value(s) of current supplied to drive means with (a) relevant reference value(s) for said current supplied and for generating a first drive-disengaging signal for controlling disengaging a relevant component from the drive means.
Because the drive means is operated at a fixed, or at least at a known, voltage, power supplied to the drive means is conveniently determined by measuring current supplied to the drive means. For the alternative motions of components of the apparatus in accordance with the invention, the current supply required by the drive means under normal circumstances can be measured and thus reference values for the required power supply can be determined and thus reference values for the required current supply are provided. Should a collision occur of any component of the apparatus with another object e.g. with another component of the apparatus, or in case of an x-ray examination apparatus with a patient that is to be examined, then the motion of the colliding component meets additional resistance and therefore the current supplied to the drive means would increase beyond said reference value. Measurement of the current supplied, and subsequently comparing with a relevant reference value provides for generating a first drive-disengaging signal for interrupting the motion of the colliding component, and thus preventing the collision to cause damage or injury.
A further preferred embodiment of an apparatus in accordance with the invention is characterized in that the arrangement for collision protection comprises a memory means for storing said reference value(s).
Reference values for current and/or power supply to drive means of the apparatus being fixed, a particularly simple way of supplying said reference values to the comparison means is to provide a memory means in which reference values can be stored and from which said reference values are supplied to the comparison means. Notably, when current supply to the drive means is compared with a relevant current reference value, the comparison means is formed by a current comparator.
A further preferred embodiment of an apparatus in accordance with the invention is characterized in that the arrangement for collision protection comprises position detection means for detecting a position of a component of the apparatus, and also comprises computing means for calculating an expected position of said component, and further comprises position comparison means for determining a difference between said detected position and said expected position and for generating a second drive-disengaging signal for controlling disengaging a relevant component from the drive means.
By comparing the actual position of a component of the apparatus to the expected position of said component, it is accurately determined if the motion of said component has been obstructed. Collision protection is achieved in that a disengaging signal is generated when the actual position deviates from the expected position in excess of a predetermined threshold value and when also the current and/or power supplied to the drive means exceeds a relevant reference value.
A further preferred embodiment of an apparatus in accordance with the invention is characterized in that the arrangement for collision protection comprises a signal processing means whereto the first and second drive-disengaging signals are supplied and said signal processing means being arranged generate a third drive-disengaging signal for controlling disengaging a relevant component from the drive means, in dependence of the first and second drive-disengaging signals.
A further refined way of detecting obstruction of a component of the apparatus consists of combinedly comparing current and/or power supply to the drive means to a reference value and comparing the detected position of said component to a corresponding expected position. Employing both current and/or power comparison and position comparison, which yield a first drive-disengaging signal and a second drive-disengaging signal, respectively, leads to reliable detection of obstruction, and hence a collision being imminent. If both first and second drive-disengaging signals indicate a collision being imminent, then a third drive disengaging signal is supplied for disengaging the drive means.
A further preferred embodiment of an apparatus in accordance with the invention, also comprising a brake, is characterized in that the arrangement for collision protection comprises brake-engaging means, and a signal processing means arranged to receive relevant drive-disengaging signal(s) and for supplying a brake-engaging signal to said brake engaging means for engaging said brake, after a predetermined period of time after receipt of said drive-disengaging signal(s).
Components of an apparatus which is balanced, are moveable without substantial effort. When a component of an apparatus in accordance with the invention and which is also balanced, is undesiredly obstructed by another component of the apparatus, or with a person within the reach of a component of the apparatus, or with a patient to be examined in the case where the apparatus is an x-ray examination apparatus, a component involved in obstruction is disengaged from the drive means by the arrangement for collision protection and by the recoil following the obstruction, the component involved in obstruction moves in a direction opposite to its direction of motion prior to the obstruction. After a predetermined period of time after generating the disengaging signal for disengaging a component involved in obstruction from the drive means, a brake-engaging signal is generated for engaging a brake, so as to stop a relevant components of the (x-ray examination) apparatus in such a position that neither a patient of another component is obstructed.
A further preferred embodiment of an apparatus in accordance with the invention is characterized in that the arrangement for collision protection comprises a speed detection means for detecting a speed of a moving component and supplying a selection signal to the memory means, for selecting a reference value in correspondence with a detected speed.
In particular when the apparatus is an x-ray examination apparatus, in various stages of an examination procedure, components of the x-ray apparatus are moved with different speeds. The required current and/or power supply is dependent on the speed with which relevant components are moved. By the speed detection means selection signals are supplied to the memory means for selecting appropriate reference values for the current and/or power supply in correspondence with the speed of moving components of the x-ray apparatus.
An apparatus comprising drive means for moving components of said apparatus and further comprising an arrangement for collision protection is characterized in that the arrangement for collision protection comprises means for determining actual values of differences between current and/or power supplies at consecutive instants to the drive means, and difference comparison means being arranged to compare (a) value(s) of (a) difference(s) between current and/or power supplied to drive means with (a) predetermined reference value(s) for said differences between current and/or power supplied and for generating a difference-excess signal for controlling disengaging a relevant component from the drive means.
Should a collision occur of any component of the apparatus with another object e.g. with another component of the apparatus, or with a person within the reach of a component of the apparatus, or in the case where the apparatus is an x-ray examination apparatus, with a patient that is to be examined, then the motion of the colliding component meets additional resistance, and therefore the rate of increase of current and/or power supply required by the drive means would increase beyond said reference value. Detection of the rate of increase of required current and/or power supply, and subsequently comparing with a relevant reference value provides for generating a signal for interrupting the motion of the colliding component, and thus avoiding the collision to cause damage or injury.
An industrial robot, e.g. for welding or for displacing parts, or an automatic manipulator, often comprises moveable components being driven by drive means. Such industrial robots are employed in circumstances where persons are within the reach of one or more of said moveable components. Therefore, providing an arrangement is called for to improve safety and to avoid malfunctioning of the industrial robot. Preferably, an industrial robot in accordance with the invention comprises an arrangement for collision protection comprising current and/or power measuring means for determining (a) value(s) of current and/or power supplied to the drive means, and comparison means for comparing said determined value(s) of current and/or power supplied to drive means with (a) reference value(s) and for generating a first drive-disengaging signal for controlling disengaging a relevant component from the drive means.
An x-ray examination apparatus often comprises moveable parts which are driven by drive means. When performing a medical examination various parts of the apparatus often are positioned close to a patient that is being examined. For example an x-ray image intensifier is preferably placed almost in contact with the patient to obtain x-ray images with good spatial resolution. In order to achieve safety for the patient and to avoid damage to the x-ray apparatus owing to a collision of parts, an x-ray examination apparatus according to the invention comprises an arrangement for collision protection comprising current and/or power measuring means to determine (a) value(s) of current and/or power supplied to the drive means, and comparison means to compare said determined value(s) of current and/or power supplied to the drive means with (a) reference value(s), and to generate or a first drive-disengaging signal for controlling disengaging a relevant component from the drive means.
The various functions which the arrangement for collision protection should execute in an apparatus in accordance with the invention, are preferably performed by a computer suitably programmed for performing said functions.